This invention relates to compact optical imaging apparatus for use, for example, in projecting an image of an information bearing document to a photoconductive member of a compact electrographic copier.
Compact electrographic copiers are designed for personal use and occupy a small space, such as a desk top for example. Such copiers typically produce latent electrostatic images of input information (e.g., a document) on the surface of a photosensitive member. The photosensitive member is, for example, insulative receiver material which has been coated with a photoconductive layer. Such material, when uniformally electrically charged and exposed to a light image of input information, has a latent image electrostatic charge pattern corresponding to such information formed on its surface. The charge pattern is developed with pigmented marking particles, which are fixed to the material to form a reproduction of the input information. However, since such coated receiver material is relatively expensive, it is becoming more popular to employ a reusable photoconductive member.
The reusable photoconductive member is uniformly electrically charged, exposed to a light image of input information to produce the latent image electrostatic charge pattern corresponding to such information, and developed with pigmented marking particles to form a transferable image. The transferable image is subsequently transferred to a receiver material and permanently fixed to the receiver material to form the reproduction. Such photoconductive member is cleaned and can be reused. The receiver material, such as a sheet of plain bond paper, is relatively inexpensive and can be disposed of when the reproduction is no longer needed.
Reduction of the size of copiers using reusable photoconductive members has been difficult to achieve due, at least in part, to the required optics. The image projected to the photoconductive member must be upright and wrong-reading to result in a right-reading reproduction. Generally, optics for accomplishing such proper image orientation have relatively long optical conjugate distances (generally, equal to twice the length of the diagonal of the optically projected image). This accordingly necessitates that the overall size of the copier be relatively large. While there are certain optical arrangements having short optical conjugate distances which orient images upright and wrong-reading at the image plane, such apparatus have critical limitations. For example, fiber optics can produce upright and wrong-reading images, but require small spacing between the entry faces of the fibers and the photoconductive member which can abrade the member. Further, resolution is limited by the fiber diameter, or laminar period, and the spacing of such fibers relative to the photoconductive member. Another relatively short optical conjugate distance optical arrangement is shown in U.S. Pat. No. 3,687,545, issued Aug. 29, 1972 in the name of Moorhusen. The apparatus of such patent still requires enough spacing for parallel lens strips and a prism. Moreover, the strips must be accurately located relative to one another in order that elements in the respective strips are coaxially alligned.